The present invention relates to a method for the preparation of a laminate or, more particularly, to a method for the preparation of a laminate based on fabric sheets of aromatic polyamide fiber laminated by use of a resinous adhesive or binder.
The invention further relates to a method for the preparation of a laminate useful, for example, as a material for substrates of printed circuit boards having a greatly improved mechanical strength and dimensional stability by increasing the adhesive bonding strength between the resin-impregnated fabric sheets forming the laminate.
Aromatic polyamide fibers are excellent in several characteristics such as low density, high strength, high elastic resilience, high heat-resistance, high flame-retardancy and so on and are very useful as a base meterial of laminates of which heat resistance is essential. The fibers, however, have a problem relative to the poor adhesive bonding strength to a resinous binder used in the preparation of prepreg sheets to be laminated so that it is eagerly desired to improve the aromatic polyamide fibers in this regard.
In order to improve the adhesion of the aromatic polyamide fibers to an adhesive or resinous binder, various proposals and experimental attempts have been hitherto made on the methods of treatment including chemical treatments in several different ways such as chemical etching, priming and the like and physical treatments such as corona discharge treatment and so on. No satisfactory results, however, have yet been obtained due to the outstandingly high stability of the aromatic polyamide fibers per se as a chemical material.